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If the hard drive in your Mac starts misbehaving, you can run Apple’s Disk Utility (or any of numerous third-party utilities) to repair it. But what if the drive in your Time Capsule develops errors—as anecdotal evidence suggests is quite common? Although Apple has not yet provided a way to repair your Time Capsule disk directly, there are a few techniques you can try that often bring a wayward disk back to life.

If Time Machine consistently reports errors when backing up to a Time Capsule, or if your backup volume won’t mount at all, here are some things you can try:

Try repairing the disk image

Time Capsule stores Time Machine backups on disk images. Although Disk Utility can’t repair the Time Capsule disk itself, it can be used on these disk images, which more often than not are the source of the problem. To check your disk image, follow these steps:

Open the Time Machine pane of System Preferences and turn off Time Machine.

Select your Time Capsule in the sidebar of any Finder window and double-click on the folder inside it (which may be named “Data” or “Backups,” or something else of your choosing) containing your Time Machine backups. If the disk doesn’t mount automatically, click on Connect As in the dialog box that appears, and supply your credentials if prompted to do so. This folder should contain one disk image for each Mac you back up with Time Machine (and nothing else).

Double-click on the disk image corresponding to the Mac that’s experiencing Time Machine errors, and wait for it to mount. This sometimes takes a while; be patient.

Open Disk Utility (in /Applications/Utilities/). In the list on the left, select the disk image. Click on the First Aid tab, and then click on Repair Disk. Disk Utility examines the disk image and—if it finds any errors it can repair—fixes them. Because Disk Utility is examining a network volume, be prepared to wait much longer than you would for a comparable repair of a local volume.

Disk Utility can't see your Time Capsule disk itself, but it can see (and often repair) the disk images that contain your Time Machine backups.

If Disk Utility finds errors that it can’t repair, a utility such as Alsoft’s $100 DiskWarrior may be able to fix the disk. It’s worth a try if you have it (or another repair program) available. If you can’t repair the disk image for one reason or another, or if the repair appears to succeed but Time Machine still won’t work, you may need a more drastic approach.

Delete the disk image

If the problem affects only a single Mac, you can try deleting that Mac’s disk image and starting over with a fresh backup (keeping in mind that in so doing, you’ll lose that Mac’s older backups). But if the problem affects all your Macs, move on to the next tip.

Erase the Time Capsule disk

If all repair attempts fail and even deleting the disk image doesn’t make Time Machine happy, you can erase the entire disk. This procedure is easy to do and solves the vast majority of Time Capsule disk problems. But there’s a price: you lose all your Time Machine backups! So, before doing this, make sure you have another backup of your data.

To erase your Time Capsule disk, follow these steps:

Open AirPort Utility (in /Applications/Utilities/) and select your Time Capsule in the list on the left.

Click on Manual Setup, click on the Disks icon on the toolbar, and then click on the Disks tab.

Select your disk (normally this is called “Time Capsule Disk”), click on Erase, and then click on Erase two more times in the confirmation dialogs that appear.

After AirPort Utility has erased your disk, Time Machine will have to perform a full (and therefore time-consuming) backup the next time it runs.

Swap out the hard drive

What if your disk appears to have errors but you can’t bear to lose all your Time Machine backups? If you’re adventurous, have some modest geek skills, and own a Time Capsule that’s no longer under warranty (or don’t mind voiding the warranty), one option is to physically remove the hard drive from your Time Capsule. (You can find instructions for dismantling your Time Capsule on the OmniNerd blog.)

Once you’ve done that, you can put the drive in an external USB or FireWire enclosure that accepts 3.5-inch SATA drives. Or, you can use an adapter such as NewerTech’s $35 USB 2.0 Universal Drive Adapter to connect it to a Mac. Once it’s hooked up, use Disk Utility (or your favorite third-party repair tool) to examine and attempt to fix the entire disk, rather than just an individual disk image. If the repair is successful, return the drive to the Time Capsule and you should be back in business. But note that if the repair fails, you must likely erase the drive and start over.